In recent years, various technologies are suggested to realize a magnetic random access memory (MRAM) using a tunneling magnetoresistive (TMR) effect or a giant magnetoresistive (GMR) effect.
The MRAM that is one of nonvolatile semiconductor memory devices has a magnetic tunnel junction (hereinafter, simply referred to as MTJ) element. In detail, the MTJ element basically has a stack structure that includes three layers of a memory layer made of a magnetization film to store data by changing a magnetization direction, a reference layer made of a magnetization film using magnetization fixed in one direction, and a tunnel junction layer (nonmagnetic layer) made of an insulating film formed between the memory layer and the reference layer. If an electric current flows to the MTJ element including the memory layer, the tunnel junction layer, and the reference layer, a resistance value of the MTJ element changes due to a change in the magnetization direction of the memory layer with respect to the magnetization direction of the reference layer caused by the TMR effect. Specifically, when the magnetization directions of the memory layer and the reference layer are parallel to each other, the resistance value becomes a minimum value and when the magnetization directions are anti-parallel to each other, the resistance value becomes a maximum value. This state is stored as information of “1” or “0”.
In the MRAM, many technologies are suggested for practical use. Because inversion of a magnetization direction by a spin-polarized current is theoretically and experimentally confirmed, an MRAM using the spin-polarized current is suggested as one of the technologies. According to the suggestion, magnetization inversion of a magnetic layer can be realized by only an amount of the spin-polarized current flowing in the magnetic layer. If the volume of the magnetic layer is small, spin-polarized electrons that are injected to invert the magnetization of the magnetic layer decrease. Therefore, it is expected that both miniaturization and a reduced current can be realized.